Liquid lactic acid is used as a natural acid in the food industry, particularly as an acidulant in the making of bread and the preparation of beverages, for acidification purposes and to improve the shelf life of foods. Its "round", fine, acid taste makes it particularly suitable for this application. However, because elaborate preparations must be made when measuring out the liquid lactic acid, it cannot be used extensively despite the advantageous taste properties. For processing reasons, naturally-solid crystalline citric acid is preferred even though it is stronger and more acid-tasting.
The natural calcium salt of lactic acid, Ca(C.sub.3 H.sub.5 O.sub.3).sub.2, has the property of adding further acids and hence forming overacidified or hyperacidified salts. Hyperacidified addition compounds of calcium lactate have been described in a number of previous publications, for example in German Reich Pat. No. 346,521, German Reich Pat. No. 414,171, and U.S. Pat. No. 2,046,610. However, it has not proved possible, thus far, to manufacture compounds containing more than 3 moles of free lactic acid per mole of calcium lactate. As a rule, only 1-2 moles of lactic acid are bonded to the known hyperacidified salts by the addition process. Calcium lactates with more than 2 moles of added lactic acids are hygroscopic, as described in German Reich Pat. No. 414,171. According to the known process, hyperacidified calcium lactates are obtained by the direct action of at least 90% lactic acid solutions on lime, calcium carbonate, or neutral calcium lactate, or they are produced in an organic solvent reaction medium according to U.S. Pat. No. 2,046,610, whereby water must be completely or largely excluded.
In the known powdered hyperacidified calcium lactates, at most 45% of the free lactic acid is available for acidification purposes. Hence, for cost reasons, this acid in its solid form is not competitive with other acidifiers and can be used economically only in exceptional cases.
Being an .alpha.-hydroxy acid, lactic acid is in equilibrium with its esters, the so-called polylactic acids with various chain lengths, or its lactide; this equilibrium is dependent on both concentration and time. Solutions having lactic acid concentrations of 90%, or more, produce polylactic acid contents of over 40% (see C. H. Holten, Lactic Acid 1971, p. 24). Hence, all calcium lactates, which are manufactured from concentrated lactic acid solutions, contain larger proportions of polylactic acids with unknown chain lengths. These products manufactured according to German Reich Pat. Nos. 346,521 or 414,171 are not uniform by comparison with the calcium trilactates and calcium tetralactates produced according to U.S. Pat. No. 2,046,610. Moreover, due to the high degree of esterification of the lactic acid, determined by their polylactic acids and lactide, such calcium lactates also have a significantly lower content of free lactic acid available for acidification purposes than is the case in the true addition compounds produced from lactic acid and neutral calcium lactate.
However, all known manufacturing processes are elaborate and expensive. Hence, despite special purifying operations, only powdered non-hygroscopic products with a maximum of 2-3 moles of free acid can be produced.
The desirability of producing solid, non-caking lactates with a high free lactic acid content therefore is clear.